1. Field of the Invention
The present invention pertains to coating substrates and particularly to coating curved substrates. More particularly, the invention pertains to the application of multilayer optical interference coatings to curved polymeric substrates.
2. Related Art
Other approaches in the art involve surface treatment and coating processes which are primarily for non-optical purposes. None of the related art known to the applicant uses shaped electrode geometry for precision coating of substrates of complex topology.
The fundamental problem in applying high performance optical interference coatings (OICs) using conventional coating materials (such as MgF.sub.2, SiO.sub.2, TiO.sub.2, etc.) to optical quality polymers (such as polycarbonate, CR-39, i.e., a specific resin, acrylic, etc.) is the basic physical property mismatches and incompatibilities between the inorganic coating materials and the organic substrate. The difference in the temperature dependent thermal expansion coefficient is particularly acute leading to very high levels of stress in such conventional coatings developed in only a few layers. Layer counts of about twenty are the practical limit for such coatings, which limits performance and design flexibility in many applications. The present invention circumvents this problem by permitting coating designs of several hundred layers to be applied to polymeric substrates of nearly any arbitrary geometry, including very thin (i.e., several mils thick) film sheet stock.